Alginate is an anionic polysaccharide harvested globally from eleven brown seaweeds. The North American variety Macrocystis pyrifera (giant kelp) and other varieties are found spanning the globe in both the northern and southern hemispheres, with the only cultivar, Saccharina japonica being developed in China, Japan, Russia, France and Korea. In industry, alginate applications of economic importance are in the fields of: dentistry (dental impressions), in the paint industry (plasticizers), in the food industry (as thickeners) and in the field of pharmacopeia (as compounding agents for tablets, capsules and as active ingredients in upset stomach preparations). It is also used extensively in burn trauma units as a protective dressing that requires no adhesive and subsequently is less painful for the burn patient on removal. It has also most recently gained fame in the theatrical and television industry when used by prosthetic makeup artists in the creation and modification of science fiction characters and masks.
Alginate hydrogel contains a co-polymer of β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) that form a mixture of homopolymer consecutive blocks (M or G) or alternating blocks (M-G-M-G- . . . ) or unequal mixtures of these blocks (M-M-G-M-G-G-M . . . ) may occur and is based upon the prevalence of each co-polymer within the seaweed itself. An example representation of the structure of co-polymer components of alginate is shown with reference to FIG. 1
As an example, variation occurs in the M to G ratio (M:G) based on the turbulence of the waters whence the brown seaweed was harvested. In turbulent waters greater flexibility and higher strength of the seaweed (higher M content) is needed to maintain anchorage by a strong holdfast (analogous to a root in plants) and flexible stipe (analogous to a stem) as compared to a tidal pool that is sheltered. In this circumstance, the stipe may require more structure (higher G content) to enable the blade (analogous to leaves in plants) to rise above the water surface enabling successful competition against green algal mats that often cover the water surface.
Other modifying factors are the temperature and the depth of the waters from where it was harvested, the age of the kelp and whether they harvested the entire kelp holdfast, stipe or blade or only a portion (e.g.: the blade). In each case, the living kelp produces the appropriate M:G ratio to maintain its ecosystem. In some cases an algal kelp forest may include other kelp species that are harvested unintentionally (some giant kelp forests include 20 other species that are largely undisturbed when only the giant kelp blade is harvested). These factors promote variation from one alginate product lot to the next and therefore a small and simple test is required to select the appropriate ionic strength concentration (salts of sodium, potassium and calcium) for creating the desired porosity. From that point forward, constancy of formulation within the lot remains the same. This is a common practice in most biological reagents as the “activity of enzymes” changes with each lot. Alginates are available and sold in United States Pharmacopeia (USP) grade that requires sufficient purity to meet or exceed that used for food, drug or medicinal use.